One of the consultants working on a project for us recently took a week off. When he returned, he found that our SharePoint Online sites in our Office 365 Tenant no longer had this file: /_layouts/15/MicrosoftAjax.js . However, he still saw the file on other Office 365 tenants that he had access to.
We promptly opened a ticket with Microsoft Premier support and found out that they removed this file, without notice, because of an update to Excel services:
the microsoftajax.js file was previously used by Excel services a while ago however has since been removed including all the references to the file. Currently it’s not being used by any real component in SPO
The suggested workaround is this:
we have identified that the, Public CDN Version of the MicrosoftAjax.js Java Script can be found at this location https://ajax.aspnetcdn.com/ajax/4.0/1/MicrosoftAjax.js
We were glad they had a work around ready, but this is yet another example of an undocumented change in Office 365. Luckily for us, our project had not gone live yet, but if it had, or worse, if we had built several solutions referencing this file, we would have had outages to deal with.
After writing this blog post and almost closing the ticket, I decided to post the same information on the Office 365 IT Pro Yammer network. I received a reply from one of the Microsoft PM’s stating that removing this file was a mistake. I then shared that Yammer post with the support engineer and Microsoft restored the file and admitted that removing it was a mistake!